Presidential candidate Edmund G. (Jerry) Brown Jr. launched a big, last-minute campaign effort in Maine this week and found himself getting assistance from a somewhat embarrassing ally -- Jimmy Carter.

To help Brown cut into Edward M. Kennedy's support among liberal Democrats in Sunday's town caucuses, Maine's secretary of state, Rodney Quinn, a leading Carter backer, gave the Brown campaign a valuable list of about 3,000 active party members statewide.

And some Carter workers gave Brown's people the names of Democrats who have been critical of the president when reached by telephone canvassers. In most campaigns, the names of such "negatives" are guarded like military secrets.

The Carter tactic is a neat example of divide and conquer. By helping Brown, the Carter camp hopes to split the anti-Carter vote and make Kennedy look weak in his native region.

But while Quinn makes no bones about what he's doing, the Carter tactic has been disconcerting for Brown. His anti-nuclear, anti-draft-registration supporters here consider dealing with Jimmy Carter to be the moral equivalent of fraternizing with the enemy.

So Brown has denied reports of an "alliance." Anyone suggesting a Brown-Carter pact, he said, was "weaving a thread of nothingness into a rug of confusion."

Brown's Maine chairman, state legislator John Michael, said Quinn's list of Democrats is open to all candidates. But Kennedy's people here said they were denied a copy.

As for Carter people providing names of "negatives," Michael said, "A personal friend of mine who's working for Carter gave me a few names, but basically that's an outrageous allegation."

Voter lists are like pure gold for Brown, who has put together in the past two weeks a statewide telephone canvass designed to find Brown supporters and turn them out.

Brown has brought a brigade of Californians -- including his parents about two dozen state officials, and an instructor from the "est" self-improvement school -- to Maine this week.

Brown said he "turned onto Maine" when he noticed that the state's small population, cheap media and active anti-nuclear and environmental communities might be made to order for his candidacy.

Brown says he wants to do well in Maine so that "the press and the voters will start listening to us for a change." But if that did happen, Brown might be chagrined: His campaigning here the past two days has been marked by inconsistencies and misstatement that probably would draw withering media comment if uttered by Kennedy or Ronald Reagan.

At a press conference in Bangor, Brown said he would eliminate the $40 billion federal deficit by "cutting every program. There's no mystery -- you cut everything across the board."

Asked if he would cut Social Security programs, Brown replied: "Well, there would have to be some exceptions." When a questioner pointed out that Social Security is the biggest item in the budget, Brown looked incredulous.

"Oh no, that's wrong," he insisted. "No way. It is not the biggest single item in the budget."

The Office of Management and Budget, in its books describing the fiscal 1981 budget, states that "Social Security is the largest single program in the budget." This has been so for years.

Speaking to students at Bowdoin College about America's "industrial decline," Brown listed a series of "incredible facts," including this one: "Next year, Toyota will sell more cars than General Motors."

Spokesmen for both firms expressed astonishment at this assertion. They said General Motors produced 5 million passenger cars and a total of about 10 million vehicles last year, while Toyota's vehicle production was under 3 million. They expect the production to be about the same next year.

Brown told a news conference Tuesday that the nuclear power share of U.S. electricity generation is "down to 7 percent and dropping." But the Department of Energy says nuclear plants accounted for 11.4 per cent of the nation's electricity in 1979 and the figure will increase slightly this year.

At most of his appearances in Maine, Brown ridiculed Carter and Kennedy for advocating weapons sales to Persian Gulf countries. But when one Bowdoin student asked him how he would respond to Soviet aggression in Afghanistan, the candidate's rambling answer included a statement that he would provide "military assistance to countries in the Persian Gulf where appropriate."

For all this, Brown's audience here -- which looked to be about 80 percent college-age or younger -- reacted warmly to his free-wheeling sallies at "crazy people" who are running the country and to his charming unpredictability.

There is something they apparently find intriguing about a presidential candidate who, in a discussion of American lifestyles, says: "I think the doughnut is among the major evils." And few other American politicians would be likely to respond as Brown did when asked why he keeps his watch set on California time. Said Brown, "That's simple: Ethnocentrism."